The present invention concerns a method for improving the operation of the disc filter, and a disc filter employing the said method. The disc filter of the invention is especially useful for removing fibers from water.
The disc filters generally employed for filtering off fibers from water consist of a number of filter discs arranged in succession on a rotating shaft and divided into several hollow filter sectors that are operationally independent of each other. Through an aperture at its apex, each sector communicates with the space inside the shaft, where a vacuum is applied. As the filter sector is immersed in the fibrous suspension to be filtered, the water starts flowing, due to the vacuum inside the shaft, through the filtering net into the filter sector, whereby the fibers contained in the water are gathered as a layer on the filtering net. Through the aperture at the apex of the filter sector, the water thus filtered then flows into a channel inside the shaft, said channel being of a length substantially equal to that of the shaft. As the disc filter rotates, all those sectors of the successively arranged discs that are in the same angular position discharge the filtered fluid into the same channel, through which the fluid is exhausted.
The disc filters currently used employ a speed of rotation of 1 rpm. To increase the capacity of the disc filter, it would be an advantage if its speed of rotation could be increased. However, this is impossible with conventional disc filters, because the filtering surfaces of the sectors do not allow enough air to penetrate through them for the water to be exhausted from the sectors and the central channel at the rate required by the higher speed of rotation. A vacuum is therefore created in the sectors during evacuation, retarding the removal of the filtered fluid from the sectors.